Reciprocating pump systems, such as sucker rod pump systems, extract fluids from a well and employ a downhole pump connected to a driving source at the surface. A rod string connects the surface driving force to the downhole pump in the well. When operated, the driving source cyclically raises and lowers the downhole plunger, and with each stroke, the downhole pump lifts well fluids toward the surface.
For example, FIG. 1 shows a sucker rod pump system 10 used to produce fluid from a well. A downhole pump 14 has a barrel 16 with a standing valve 24 located at the bottom. The standing valve 24 allows fluid to enter from the wellbore, but does not allow the fluid to leave. Inside the pump barrel 16, a plunger 20 has a traveling valve 22, which allows fluid to move from below the plunger 20 to the production tubing 18 above, but does not allow fluid to return from the tubing 18 to the pump barrel 16 below the plunger 20. A driving source (e.g., a pump jack or pumping unit 26) at the surface connects by a rod string 12 to the plunger 20 and moves the plunger 20 up and down cyclically in upstrokes and downstrokes to lift fluid to the surface.
Various types of valve assemblies have been used for the standing and traveling valves of a downhole pump. For example, FIG. 2A illustrates a one-piece valve assembly 30A according to the prior art, which can be used for a standing valve or a traveling valve of a downhole pump. The assembly 30A includes a housing 40 having uphole and downhole ends 44 and 46 with a flow passage 42 therethrough. The ends 44 and 46 have threads for threading to other components of a pump system. An internal cage 50 is integrally machined inside the flow passage 42. A ball (not shown) inserts in the internal cage 50, and a seat (not shown) inserts in the flow passage 42 to engage an internal shoulder 55. A pin-threaded component can then thread to the thread at the housing's downhole end 46 to retain the seat and ball in the cage 50.
The cage 50 includes a stop 52 to stop the ball and include flutes 54 in the flow passage 42 that allow flow to pass the ball when engaged with the stop 52. Axial rails or ball guides 56 between the flutes 54 provide support for the ball in its movement.
Being integral, the housing 40 and internal cage 50 are composed of the same material. In many cases, they are made of a stainless steel, a nickel-copper alloy, MONEL® metal, or the like. (MONEL is a registered trademark of HUNTINGTON ALLOYS CORPORATION.) It is common to line the rails 56 and even the stop with 52 with a cobalt-chromium alloy, such as a STELLITE® material, to provide hardness for supporting and engaging the ball. (STELLITE is a registered trademark of KENNAMETAL INC.) A welding process, such as tungsten inert gas (TIG) welding, is used to line the hardening alloy on the surfaces, which can be complicated.
As can be seen from this example in FIG. 2A, forming the internal cage 50 and making threads 44, 46 requires a considerable amount of machining and manipulation. Coating internal surfaces of the cage 50 with a hard alloy requires additional manufacturing and precision.
Rather than a one-piece assembly, multi-piece assemblies can be used. For example, FIG. 2B illustrates one type of two-piece valve assembly 30B according to the prior art, which can be used for a standing valve or a traveling valve of the downhole pump. Again, the assembly 30B includes a housing 40 having uphole and downhole ends 44 and 46 with a flow passage 42 therethrough. The ends 44 and 46 have threads for threading to other components of a pump system.
An insert 60 is separately machined and inserted inside the flow passage 42 to engage its upper end 64 against a shoulder 45. A ball B inserts in the insert 60, and a seat 70 inserts in the flow passage 42 to engage the lower end 66 of the insert 60. To provide sealing, a spacer 72 with a seal 74 fits against the seat 70. A pin-threaded component can then thread to the downhole end 46 to retain the spacer 72, the seat 70, the ball B, and the insert 60.
The insert 60 includes a stop 62 to stop the ball B and includes flutes 65 in the flow passage 42 that allow flow to pass the ball B when engaged with the stop 62. Axial rails or ball guides 67 between the flutes 65 provide support for the ball B in its movement. Because the insert 60 is a separate component, it can be made of a different material than the housing 40 and can be made, for example, of a STELLITE® material.
The spacer 72 and the seal 74 are needed because fluid can leak past the end 66 of the insert 60 engaged on the seat 70 and can leak around the outside of the seat 70. For example, if the assembly 30B is used as a traveling valve in a downhole pump, fluid at higher pressure in the plunger during an upstroke may leak to the lower pressure of the barrel. This leakage, if allowed to enter the threads at the downhole end 46, can erode the threads of the pump during operation. The spacer 72 with the seal 74 helps reduce leakage.
The components of the insert 60, the seat 70, and the spacer 72 are all sandwiched against the shoulder 45 by the threading of an adapter at the housing's downhole end 46. This can produce compressive load on the insert 60, which can lead to distortion and failure. For this reason, this insert 60 has an increased wall thickness to handle the compressive load, which requires the assembly 30B to be used with a ball B smaller than a standard API-sized ball.
FIG. 2C illustrates another type of two-piece valve assembly 30C according to the prior art, which can be used for a standing valve or a traveling valve of the downhole pump. This assembly 30C is for use with a standard API-sized ball. Again, the assembly 30C includes a housing 40 having uphole and downhole ends 44 and 46 with a flow passage 42 therethrough. The ends 44 and 46 have threads for threading to other components of a pump system.
An insert 60 is separately machined and inserted inside the flow passage 42 to engage its lower end 66 against a shoulder 45. To retain the insert 60 and provide sealing, a gasket 63 is placed on the upper end of the insert 60, and an adapter 41 of the housing 40 threads to the uphole threads 44. To complete the assembly, a ball (not shown) inserts in the insert 60, and a seat (not shown) inserts in the flow passage 42 to engage the shoulder 45. A pin-threaded can then thread to the thread at the housing's downhole end 46 to retain the seat and ball in the housing 40.
The insert 60 includes a stop 62 to stop the ball and include flutes 65 in the flow passage 42 that allow flow to pass the ball when engaged with the stop 62. Axial rails 67 between the flutes 65 provide support for the ball. Because the insert 60 is a separate component, it can be made of a different material than the housing 40 and can be made, for example, of a STELLITE® material.
Because the insert-style assemblies 30B-C of FIGS. 2B-2C require the insert 60 to be both securely captivate and sealed in the flow passage 42, the typical method is to incorporate additional threaded members and to tighten them to sandwich the insert 60 against a housing shoulder 45. The compressive load placed on the insert 60 can lead to increased chances of failure and can disport its shape. For these and other reasons, such insert-style design has its drawbacks such as leaking, high temperature limitations, and manufacturing costs.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.